Ivermectin toxicosis in three adult horses.

This research article explores the effects of ivermectin toxicosis in three adult Quarter Horses which presented acute neurological signs after receiving an oral administration of 1.87% ivermectin paste. The horses were treated with supportive care and although two horses survived, one horse had to be euthanized. The research suggests that ivermectin toxicosis should be considered as a potential cause when horses show acute neurologic impairment after the administration of ivermectin.

Study Overview

• The authors conducted a study on three adult Quarter horses that exhibited acute and progressively worsening neurological symptoms after being administered a single dose of 1.87% ivermectin paste.
• The observed symptoms included depression, lack of coordination in the front and hind limbs, drooping of the lips, muscle spasms, dilated pupils, reduced pupillary light responses, and absence of menace reflexes (the blink reflex which is a reaction to a fast approaching object).
• The severity of these signs increased over a 36-hour period post-administration of the drug.

Clinical Intervention

• All three horses were treated supportively with intravenous fluid administration and anti-inflammatory medications.
• Despite these measures, one horse had to be euthanized. Post-death examination found high concentrations of ivermectin in its brain tissue.
• The two other horses survived without any obvious long-term effects.

Findings

• In analyzing the ivermectin concentration in the paste product, the researchers found that its concentration was roughly what the label indicated.
• This research highlights ivermectin toxicosis as a rarely reported condition in equines or horses that should potentially be considered when horses show rapid neurological impairment after the administration of ivermectin.
• The researchers conclude that recovery from ivermectin toxicosis is possible with supportive care and time, although in severe cases, as in this study, euthanasia may be necessary.